Box hold down system

ABSTRACT

A lateral edge of a bulk bin is pivotally mounted on the subjacent side edge of a flat bed trailer, thereby enabling the bin contents to be dumped laterally as the nether side of the bin is elevated. The pivot pin extends the entire length of the bin and projects fore and aft therefrom. The pin is journaled in a sleeve mounted centrally on the side edge of the flat bed, whereas the bin is hinged to the pin along substantially the entire length of the bin. The &#39;&#39;&#39;&#39;floating&#39;&#39;&#39;&#39; fore and aft extensions of the pin and adjacent corners of the bin are constrained in their vertical motion by snubbing means mounted on the ends of the flat bed and attached to the pin extensions. Selectively operable latch means hold down the nether corners of the bin.

United States Patent [1 Norton et al.

[ BOX HOLD DOWN SYSTEM [75] lnventors: Morrison K'ai Norton; LawrenceRaymond Timko, both of Woodland, Calif.

[73] Assignee: Titan Trailer Corp.

[22] Filed: Sept. 22, 1972 [21] Appl. No.: 291,328

2,603,531 7/1952 Gustafason 298/18 1,837,308 12/1931 Winter i 298/l7.62,160,789 5/1939 Severinghaus.... 298/18 2,394,153 2/1946 Correa 298/181 Mar. 26, 1974 Primary EQraminerRichard J. Johnson Attorney, Agent, orFirm-Lothrop & West [57] ABSTRACT A lateral edge of a bulk bin ispivotally mounted on the subjacent side edge of a flat. bed trailer,thereby enabling the bin contents to be dumped laterally as the netherside of the bin is elevated. The pivot pin extends the entire length ofthe bin and projects fore and aft therefrom. The pin is jowrnaled in asleeve mounted centrally on the side edge of the flat bed, whereas thebin is hinged to the pin along substantially the entire length of thebin. The: floating fore and aft extensions of the pin and adjacentcorners of the bin are constrained in their vertical motion by snubbingmeans mounted on the ends of the flat bed and attached to the pinextensions. Selectively operable latch means hold down the nethercorners of the bin.

14 Claims, 15 Drawing Figures PATENTEDHARZB 1974 3,799.61 2

saw 2 or 5 V wllllllllllllllllln@i PATENTED HARZG I974 SHEET 5- BF 5 BOXHOLD DOWN SYSTEM The invention relates to improvements in trailermountedsystems for attaching, transporting and emptying bulk binsof the sidedelivery type. The patent literature, as well as the market place, isreplete with devices capable of dumping boxes carried by a truck ortrailer, both being termed a trailer, for convenience herein.

The rapidly expanding field of bulk bin hauling, with its attendanteconomies of operation, has led to a proliferation of trailer-bulk boxcombinations.

Owing to the fact, however, that trailers are normally constructed witha central upwardly convex bow, unique problems are presented when bulkbins are pivotally mounted fore and aft along one of the side edges of atrailer so as to afford side dumping capabilities. The convex bow, in afore and aft direction, is built into the, frame so that when thetrailer is loaded to its cus tomary capacity, the extent of the upwardbow (amounting in unloaded condition to approximately inches at thetransverse mid-plane of the flat bed) will decrease to about zero. By soconstructing the trailer, a negative deflection, or swayback, isobviated when the trailer is fully loaded. The bins, or boxes, supportedon the trailer beds are large in size (for example, 8 feet X feet X 24feet) and must be capable of dealing with bulk cargo arnounting to manytons. Since the bulk containers possess very considerable beam strengthand rigidity, the extent of relative vertical flexure, or

movement, between the flat bed and the customary bulk container betweenloaded and unloaded conditions is often very substantial. Thus, the sideedge hinges heretofore utilized to hinge the box to the bed,particularly the hinges at the forward and after corners, have beensubject to great stresses, quickly leading to rupture of the fasteningsholding the respective hinge members to the relatively moving bed andbin as repeated cycles of loading and unloading occur. Rupture producingstresses have also occurred at the corner hinges when the nether side ofthe bin is lifted with the crane hook off-center in a fore and aftdirection.

, Efforts have heretofore been made to reduce the extent of stressimposed upon the bolts, rivets or other fasteners holding the hinged binand bed together. These attempts, for the most part, have involved theelimination of the hinge connections adjacent the forward and aftercorners of the flat bed and the superposed box. However, when haulingover uneven terrain or when traveling at considerable speed along abumpy roadway, very destructive buffeting of the box floor against theunderlying ends of the flat bed can occur when the corners are not helddown, particularly under circumstances giving rise to resonantvibrations.

It is therefore an object of the invention to provide a box hold downsystem which substantially eliminates both the rupture of hingeconnections as well as the bouncing and buffeting which has heretoforetaken place as a box is loaded and deflected from its initial positionrelative to the supporting flat bed of a truck or trailer and isthereafter transported to its destination in It is yet a further objectof the invention to provide a box hold down system which is quickly andeasily in stalled and operated, even by relatively unskilled personnel,yet is safe and reliable.

It is another object of the invention to provide a box hold down systemwhich minimizes shock and substantially eliminates any vibration of aharmful nature either to the trailer, the bin or the cargo.

It is still another object of the invention to provide a box hold downsystem which is compact, readily serviced and does not unduly protrudebeyond the margins of the bin and trailer combination.

It'is another object of the invention to provide a generally improvedbox hold down system.

Other objects, together with the foregoing, are attained in theembodiment described in the following descriptionand shown in theaccompanying drawings, in which:

FIG. 1 is a left rear perspective view showing a typical installation of.a bulk container pivotally mounted on a flat bed trailer for sidedelivery of the contents, the container being shown in lowered position;

FIG. 2 is a fragmentary perspective view, to an enlarged scale, of thehinge structure shown in FIG. 1;

FIG. 3 is a fragmentary sectional view, to a greatly enlarged scaletaken through one of the two aligned hinge sleeves mounted on a sideedge of the trailer body, the plane of the section being indicated bythe line 33 in FIG. 2;

FIG. 4 is a fragmentary sectional view,'to a greatly enlarged scale,taken through the central hinge collar mounted on a lateral lower edgeof the box, the plane of the section being indicated by the line 4-4 inFIG.

FIG. 5 is a fragmentary sectional view, to a greatly enlarged scale,taken through one of two aligned hinge rings mounted on the deflectorgate, the plane of the section being indicated by the line 55 in FIG. 2;

FIG. 6 is a fragmentary sectional view, to a greatly enlarged scale,taken through a typical portion of the hinge pin, the plane of thesection being indicated by the line 6-6 in FIG. 2;

FIG. 7 is a fragmentary left rear perspective view comparable to FIG. 1but showing a shock absorber installed on the hold down arms anddisclosing the gate in open position;

FIG. 8 is a fragmentary sectional view, to a greatly enlarged scale, ofthe snubbing mechanism, taken on the plane indicated by the line 8-8 inFIG. 7;

FIG. 9 is a fragmentary right rear perspective view;

FIG. 10 is a fragmentary rear elevational view, to an enlarged scale, ofthe pneumatically operated bin locking mechanism shown in FIG. 9, withportions of the figure broken away to reveal underlying details;

FIG. 11 is a fragmentary perspective view, to an enlarged scale, of thecrane lifting hook ring in base position as appears in FIG. 9, the ringbeing supported on the actuating arm of the air valve;

FIG. 12 is a fragmentary perspective view, to an enlarged scale, of theright hand one of the rigging anchors shown in FIG. 9, the left handanchor being a mirror image thereof;

FIG. 13 is a fragmentary perspective view, to an enlarged scale, of thecenter anchor of the crane rigging;

FIG. 14 is a rear elevational view showing the bin in a typical elevatedposition, preparatory to being returned by the crane to lowered, orbase, position;

FIG. 15 is a diagram of the pneumatic bin latching system showing theair supply, air valve and pneumatic cylinder.

While the box hold down system of the invention is susceptible ofnumerous physical embodiments, depending on the environment andrequirements of use, substantial numbers of the herein shown anddescribed embodiment have been made, tested and used, and all haveperformed in an eminently satisfactory manner.

The box hold down system of the invention, generally designated by thereference numeral 16, connects an elongated bulk cargo bin 17 to thebody 18, or chassis, of a trailer 19, or truck, supported on groundengaging wheels 21 and including, in the trailer shown in FIG. 1, a pairof front support posts 22. When in use, the forward end of the trailerwould be supported on a truck fifth wheel, or comparable structure, notshown.

The bin 17 is strongly constructed of conventional frame members, suchas angles and channels, with panels of plywood attached thereto, forming(see FIG. 1), a forward wall 24, an after wall 25, a left sidewall 26, aright sidewall 27 and bottom 28. The left sidewall 26 is hinged at thetop to a hinge 30 on an upper fore and aft box channel 20, and the wall26 can, if desired, be divided into two or more separately swingableportions, or doors.

The bottom 28 of the bin 17 is supported on the flat bed 31 of thetrailer body, with the bottom margins of the box in substantial registerwith the subjacent margins of the trailer. That is to say, the lower,left-hand lateral edge 32 of the bin 17 immediately overlies thesubjacent fore and aft lateral side 33 of the flat bed 31, and the aftertransverse lower edge 34 of the bin overlies the after end 35 of thesubjacent flat bed 31. In like fashion, the opposite side edge 36 andforward edge 37 of the box 17 overlies the corresponding right-hand sideedge 38 and forward edge 39 of the flat bed, as shown.

The lower left-hand lateral edge 32 of the bin 17, as in FIG. 1, ispivotally mounted on the lateral side 33 of the flat bed by a fixedhinge, generally designated by the reference numeral 41, the hinge 41being located approximately midway between the opposite ends, as appearsmost clearly in FIGS. 1 and 2. The central hinge 41 includes an angleiron 42 (see FIGS. 2 and 3) secured, as by bolts 43 to the upper cornerof a fore and aft channel 44 forming the lateral side edge 33 of theflat bed 31. Mounted on the horizontal flange 45 of the angle iron, asby welding, is a pair of aligned, spaced, fore and aft sleeves 46.

Journaled in the two fixed hinge sleeves 46 is a fore and aft pivot pin47, or hinge pin, extending the entire length of the box 17, andthe'underlying flatbed 31. The pin 47 also somewhat protrudes beyond theends of the box in both a fore and aft direction. The forward extension48 and the after extension 49 of the pivot pin 47 are journaled,respectively, in a forward bearing 50 and an after bearing 51.

Loosely encompassing the pin 47 is a central collar 52 welded to a framechannel of the adjacent side panel 26, thereby hinging the box forpivotal movement relative to the flat bed. The pin 47 can be a heavy rodor a strong pipe.

The bearings 50 and 51 are floating in the sense that they arevertically movable within a limited arc whose radius is defined, in thecase of each bearing, by a spaced pair of radius arms 53 secured attheir distal ends to the respective one of the journal bearings 50 and51 (each journal bearing being a mirror image of the other). The arms 53are mounted at their proximal ends on the extremities of a hollowcross-shaft 54 snugly gripped by a resilient, high-friction bushing 56of elastomeric material. The bushing 56, in turn, is tightly confinedwithin a shell 57 (see FIG. 8) secured by fastenings 58 to a bracket 59mounted on the after sides of a horizontal transverse upper channel 61and a transverse lower channel 62 mounted on the transverse end channelof the flat bed 31.

By frictionally resisting rotation of the cross-shaft 54, the radiusarms 53 are constrained to oppose and move slowly in response to anyforces tending to displace the pivot pin 47 vertically upwardly ordownwardly. Also, tending to resist upward movement of the distal endsof the radius arms is a shock absorber 66, or leveler, (see FIGS. 7 and8). The leveler 66 is pivotally mounted at its lower, distal end on aclevis 67 depending from the lower portion of the bearing 51 andpivotally mounted at its upper, proximal end on a clevis 68 mounted onand upstanding from the bushing shell 57.

Thus, although both the forward end and the after end of the pivot pin47 are not constrained by a fixed hinge, such as .the rigid center hinge41, the combination of the downward force exerted at each end of thepivot pin by the respective levelers 66 and the frictional resistanceprovided by the elastomeric bushings 56, is effective to prevent the endportions of the bin 17 from vibrating and striking against the subjacentflat bed surface.

A first collar 71 mounted on the bin 17 loosely encircles the pivot pin47 adjacent the forward bearing 50 and a similar collar 71 is providedadjacent the after bearing 51. The collars 71 serve to connect the twofloating adjacent ends of the bin to the pivot pin 47 while the maincentral hinge 41 secured to the flat bed rigidly maintains the centralportion of the bin in fixed vertical position relative 'to the bin whilesimultaneously allowing the bin to pivot about the hinge pin 47 as thebin is emptied. The two collars 82 augment the collars 71.

By thus allowing the fore and aft ends of the pivot pin 47 to float, theadjacent end portions of the bin can deflect vertically upwardly anddownwardly relative to the central portion of the box when loading andunloading of the bin contents takes place. Hinge rupture is therebyobviated. In other words, by allowing the ends of the box and the pivotpin to float relative to the trailer ends, no disruptive forces occur asa result of relative displacement occasioned by loading and unloading.At the same time, the hold-down effort exerted on each end of the box bythe levelers, and the cushioning effect of the frictional elastomericbushings maintains control over the floating ends of the pivot pin andthe box, thereby obviating vibration and harmful buffeting against thesubjacent portions of the flat bed.

The lower portion of the left-hand side panel 26 of the box includes adeflector gate, generally designated by the reference numeral 74including an elongated plate 76 welded to a top longitudinal element ofthe pivot pin 47. The upper margin of the plate 76 is bent outwardly toform a lip 77 and at theopposite ends of the gate a pair of sectorplates 78 overlying the end panels 24 and 25 and suitably latchedoperating levers 79 are mounted. The somewhat laterally yielding leversare releasably held by cam faced latch plates 80 (see FIGS. 1, 2 and 7)on the nearcorner posts of the bin.

The gate 74 is welded to the pivot pin 47, as appears most clearly inFIG. 6, and includes a pair of rings 81 interposed between the sleeves46 and the central collar 52. The bottom of the plate 76 is providedwith a plurality of suitable accommodating apertures 83 to allow thecentral collar 52 and the collar pairs 71 and 82 encompassing the pin 47to protrude through the plate and be connected to the adjacent fore andaft box channel. A comparable pair of apertures 84 in the plate 76 (seeFIG. 3) allows relative motion between the pin 47 and plate 76 structureand the fixed sleeves 46. If preferred, the gate 74 can be hinged to thepivot pin 47 by omittingthe weldments between the pin 47 and the gate74, asrindicated in FIG. 6, thereby allowing relative angular movementbetween the pin 47 and the looselyencompassing rings 81 secured to thegate 74, as appear most clearly in FIG. 5.

The gate 74 enables the contents of the box to be discharged through anelongated fore and aft opening 86 in the bottom portion of the left-handside panel 26 (see FIG. 7) covered by the gate 74 when the gate isclosed. When the contents are to be discharged, the nether, orright-hand, side of the bin is suitably elevated, as will be explainedsubsequently in more detail, and the hinged gate 74 is opened byunlatching and appropriately manipulating the operating levers 79. Theplate 76 of the gate 74, when in open position, serves as a deflectorapron, directing the bin contents laterally outwardly, well beyond thelateral side edge of the trailer and the supporting wheels. This featureis particularly valuable where the contents are of a soft nature, suchas peaches or tomatoes, which are preferably kept out of the path of thetrailer to avoid slippery conditions. When the box is elevated, thehinged side panel 26 also swings outwardly, by force of gravity,pivoting about the hinge 30. The open gate 74 and the side panel 26 forma converging channel 40 effective to guide the emerging contents in alateral direction (see FIG. 14).

As will be appreciated, it is not only desirable that the ends of thebox on the hinge side (left-hand side in FIG. 14) be free, withinlimits, to float, but also that the nether, or right-hand side beprovided with somewhat similar capabilities. Thus, even though theright-hand side of the box is locked down during all conditionsexceptunloading, by suitable lock mechanisms now to be described, boththe forward and the after ends. of the box on the right-hand side canmove, within small limits, and under constraint, relative to thesubjacent portions. of the flat bed.

Locking engagement between the nether corners of the bin and the flatbed is effected, at each end, by a latch mechanism 86 (see FIGS. 1, 9and 10) comprising a rockable latch hook 87 pivoted on a pivot pin 88and actuated by a pivotally-mounted plunger 89 in association with apneumatic cylinder 90 of the kind used, for example, in connection withthe air brakes of a motor vehicle. I

When the plunger 89 is extended, the latch hook 87 partially encircles apin type of latch detent 91, or latch mounted on a transverse lower rearframe member 93 of the bin. The pin detent 91 is also secured at itsafter end to a downturned, L-shaped, member 94 projecting rearwardlyfrom and connected to the angle iron 92 and the bin frame member 93.

The angle iron 92, the L-shaped bracket member 94 and the detent latchpin 91, in other words, are attached to the bin whereas the latch hook87 is connected to the flat bed. Thus, when it is desired to lift thebox into emptying position, the hook 87 is withdrawn from the latch pin91 by retracting the plunger 89 into the cylinder 90.

This unlatching motion is automatically effected as the crane hookrigging ring 96 is lifted off the vertically movable upwardly biased airswitch located just above the ring-supporting hook 97 (see FIGS. 9, 11and 15), the switch 95 being connected to an air valve 98 interposed inan air supply line 99 extending from a pressurized air tank 101 to thepneumatic cylinder90.

The air valve actuator 95 is so connected to the air valve 98 that inthe base position shown in FIGS. 9 and 11, the weight of the ring 96 andattendant wire cables 103, leading from the central lower anchor 104 andextending angularly downwardly to the forward anchor 106 and afteranchor 107, is sufficient to overcome upward bias and depress the valueactuating switch 95 so as to keep the air valve 98 in open or lockedposition.

When it is desired to tilt the bin into unloading position, however, andthe crane hook ring 96 is lifted off the vertically movable,spring-loaded valve actuator 95 and supporting hook 97 in order toattach the lifting ring 96 to the crane hook 111 (see FIG. 14) thespringloaded valve actuator 95 moves upwardly, allowing thespring-loaded air valve 98 to close so as to release the actuating airpressure on the plunger 89 and allow the internal return spring (notshown) to act and thereby unlatch the hook 87 from the latch pin 91.

After the hook 87 is thus unlatched, the crane hook 111 is attached to alifting crane by which the bin can be elevated, thereby lifting thenether side of the bin and tipping the bin and allowing the contents tospill out through the channel defined by the deflector gate 74(previously or concurrently opened) and the gravity actuated door 26.The channel formed by the door 26 and the gate permits dumping of thecontents without unduly tilting the bin and also deflects the contentslaterally, well clear of the discharge side of the trailer.

After the contents are emptied, the crane hook is again lowered so thatthe bin can settle back into position on the flat bed. The crane hookring 96 is thereupon removed from the crane hook 111 and returned to thevalve actuator 95 and attendant support hook 97, the weight of therigging depressing the actuating lever 95, thereby causing the air valveto open and translating the plunger 89 so as to return the latch hook 87into hold-down engagement with the detent pin 91, thereby completing thecycle.

As appears most clearly in FIG. 10, the latch hook face in engagementwith the detent pin is so shaped that the air pressure on the latch hooktends constantly to cam or bias the hook 91 in a downward direction. In

other words, the inner curvature 1100 of the latch hook 87 is such thatthe strong pneumatic force urging the latch hook 87 into engagement withthe latch pin 91 tends to force the latch pin 91 downwardly, therebyresisting upward bouncing movement ofthe adjacent box corner. Yet, owingto the hook curvature, some slight freedom is afforded so that the latchhook 87 can move up and down to a small degree, with respect to therelatively small vertical reciprocations of the latch pin 91. Rupture ofthe engaging members is thereby obviated. This same yielding resistanceto relative movement also prevents rupture as loading and unloading ofthe cargo takes place.

it can therefore be seen that we have provideda box hold down system foruse with a bin-trailer combination which is not only capable ofeliminating the vibration and structural ruptures heretoforeencountered, but which is also safe, efficient, economical and longlived in operation.

What is claimed is:

1. In combination with a trailer including a flat bed with a pair offore and aft side edges and a pair of transverse ends, a box hold downsystem comprising:

a. ahinge carried on one of saidside edges, said hinge including asleeve mounted on said one of said side edges intermediate said ends ofsaid trailer, and a pivot pin joumaled in said sleeve and extendinglongitudinally adjacent said one of said side edges of said flat bed;

b. a box supported on said flat bed in a first lowered position, thelateral edge of said box adjacent said one of said side edges beingpivotally connected to said hinge,.said pivot pin extendinglongitudinally adjacent said lateral edge of said box, said box beingpivotally mounted on said pin and angularly movable between said firstlowered position and a second elevated position laterally to dischargethe contents of said box;

c. snubbing means mounted on said transverse ends adjacent said one ofsaid side edges and connected to the adjacent corners of said box forresiliently opposing the upward movement of said lateral edge of saidbox, said pin including a forward extension and an after extensionprojecting beyond the respective forward end and after end of said flatbed, said pin extensions being connected to said snub bingmeans; and,

d. latch means mounted on said ends of said flat bed adjacent the otherof said side edges and connected to the adjacent corners of said box fordetachably holding down said box.

2. A box hold down system as in claim 1 in which said snubbing meansincludes a bushing of resilient material having a high coefficient offriction, a shaft rotatably mounted on said bushing in frictionallyresistant engagement therewith; a lever arm mounted at one end on saidshaft and pivotally connected at the other end to the adjacent one ofsaid pin extensions.

3. A box hold down system as in claim 2 including a spring biasedleveler adjacent each of said snubbing means, one end of said levelerbeing mounted on the adjacent of said transverse ends and the other endof said leveler being mounted on the adjacent of said pin extensions.

4. A box hold down system as in claim 1 in which said latch meansincludes a latch detent on each of said adjacent corners of said box; alatch hook pivotally mounted on said ends of said flat bed adjacent saidother of said side edges for selective engagement with and disengagementfrom said detent; and pneumatic means for selectively connecting anddisconnecting said latch hook from said latch detent.

5. A box hold down system as in claim 4 wherein said pneumatic meansincludes a plunger pivotally connected to said latch hook; a pneumaticcylinder operatively engaging said plunger; a pressurized air supplyconnected to said cylinder; and valve means connected to said air supplyfor remotely controlling the operation of said cylinder and said plungerto effect latching and unlatching of said hook.

6. A box hold down system as in claim 1 in which one side of said boxincludes a gate extending along said lateral edge of said box, said gatebeing connected to said pivot pin.

7. A box hold down system as in claim 6 wherein said gate includes afore and aft elongated plate mounted on said pivot pin; and a gateoperating lever mounted on said pin, said lever being capable ofswinging said gate between a closed position covering an elongatedopening in the bottom of said one of said walls adjacent said lateraledge of said box and an open position uncovering said opening.

8. A box hold down system as in claim 6 including a door hingeablymounted on said one side of said box, said door being capable of openingoutwardly by gravity and forming with said gate in said open position alaterally outwardly converging cargo channel.

9. In a trailer having a flat bed with a pair of fore and aft side edgesand transverse ends, a system for holding down a box carried on thetrailer comprising:

a. a hinge mounted on one of the side edges of the flat bedsubstantially centrally between the transverse ends, one lateral edge ofthe box being connected to said hinge for tilting movement between afirst lowered position and a second elevated position, the comers of thebox located fore and aft from said hinge being sufficiently remote fromsaid hinge as to be substantially responsive to forces tending to movethe box corners vertically relative to the subjacent flat bed during useof the trailer;

b. snubbing means mounted on the trailer and connected to the box forresiliently opposing movement of said boxcorners; and

c. latch means mounted on the trailer and connected to the box fordetachably securing the other lateral edge of the box to the flat bed.

10. A box hold down system as in claim 9 in which said latch meansincludes alatch detent mounted on the box, a latch hook pivotallymounted on the flat bed adjacent the end of said other lateral edge ofthe box for selective engagement with and disengagement from saiddetent, and means for selectively connecting and disconnecting saidlatch hook from said latch detent.

11. A box hold down system as in claim 9 including a door hingeablymounted along the upper portion of the side of the box adjacent saidhinge, said door being capable of opening outwardly to provide a chm forthe discharge of cargo as the box is tilted upwardly from said firstlowered position toward said second elevated position.

12. A box hold down system as in claim 9 in which the side of the boxadjacent said hinge includes a gate extending along said one lateraledge of the box, said gate being movable between a closed positioncovering an elongated fore and aft opening along the lower portion ofsaid box side and an open position uncovering said opening.

I means adjacent said corners for resiliently opposing relative verticalmovement between said corners and the underlying surface of the flatbed.

14. A box hold down system as in claim 13 including a shock abosrbermounted on at least one end of the trailer and connected to the adjacentend of said pin, said shock absorber being inclined at an attitude suchas to oppose upward vertical movement of said pin.

1. In combination with a trailer including a flat bed with a pair offore and aft side edges and a pair of transverse ends, a box hold downsystem comprising: a. a hinge carried on one of said side edges, saidhinge including a sleeve mounted on said one of said side edgesintermediate said ends of said trailer, and a pivot pin journaled insaid sleeve and extending longitudinally adjacent said one of said sideedges of said flat bed; b. a box supported on said flat bed in a firstlowered position, the lateral edge of said box adjacent said one of saidside edges being pivotally connected to said hinge, said pivot pinextending longitudinally adjacent said lateral edge of said box, saidbox being pivotally mounted on said pin and angularly movable betweensaid first lowered position and a second elevated position laterally todischarge the contents of said box; c. snubbing means mounted on saidtransverse ends adjacent said one of said side edges and connected tothe adjacent corners of said box for resiliently opposing the upwardmovement of said lateral edge of said box, said pin including a forwardextension and an after extension projecting beyond the respectiveforward end and after end of said flat bed, said pin extensions beingconnected to said snubbing means; and, d. latch means mounted on saidends of said flat bed adjacent the other of said side edges andconnected to the adjacent corners of said box for detachably holdingdown said box.
 2. A box hold down system as in claim 1 in which saidsnubbing means includes a bushing of resilient material having a highcoefficient of friction, a shaft rotatably mounted on said bushing infrictionally resistant engagement therewith; a lever arm mounted at oneend on said shaft and pivotally connected at the other end to theadjacent one of said pin extensions.
 3. A box hold down system as inclaim 2 including a spring biased leveler adjacent each of said snubbingmeans, one end of said leveler being mounted on the adjacent of saidtransverse ends and the other end of said leveler being mounted on theadjacent of said pin extensions.
 4. A box hold down system as in claim 1in which said latch means includes a latch detent on each of saidadjacent corners of said box; a latch hook pivotally mounted on saidends of said flat bed adjacent said other of said side edges forselective engagement with and disengagement from said detent; andpneumatic means for selectively connecting and disconnecting said latchhook from said latch detent.
 5. A box hold down system as in claim 4wherein said pneumatic means includes a plunger pivotally connected tosaid latch hook; a pneumatic cylinder operatively engaging said plunger;a pressurized air supply connected to said cylinder; and valve meansconnected to said air supply for remotely controlling the operation ofsaid cylinder and said plunger to effect latching and unlatching of saidhook.
 6. A box hold down system as in claim 1 in which one side of saidbox includes a gate extending along said lateral edge of said box, saidgate being connected to said pivot pin.
 7. A box hold down system as inclaim 6 wherein said gate includes a fore and aft elongated platemounted on said pivot pin; and a gate operating lever mounted on saidpin, said lever being capable of swinging said gate between a closedposition covering an elongated opening in the bottom of said one of saidwalls adjacent said lateral edge of said box and an open positionuncovering said opening.
 8. A box hold down system as in claim 6including a door hingeably mounted on said one side of said box, saiddoor being capable of opening outwardly by gravity and forming with saidgate in said open position a laterally outwardly converging cargochannel.
 9. In a trailer having a flat bed with a pair of fore and aftside edges and transverse ends, a system for holding down a box carriedon the trailer comprising: a. a hinge mounted on one of the side edgesof the flat bed substantially centrally between the transverse ends, onelateral edge of the box being connected to said hinge for tiltingmovement between a first lowered position and a second elevatedposition, the corners of the box located fore and aft from said hingebeing sufficiently remote from said hinge as to be substantiallyresponsive to forces tending to move the box corners vertically relativeto the subjacent flat bed during use of the trailer; b. snubbing meansmounted on the trailer and connected to the box for resiliently opposingmovement of said box corners; and c. latch means mounted on the trailerand connected to the box for detachably securing the other lateral edgeof the box to the flat bed.
 10. A box hold down system as in claim 9 inwhich said latch means includes a latch detent mounted on the box, alatch hook pivotally mounted on the flat bed adjacent the end of saidother lateral edge of the box for selective engagement with anddisengagement from said detent, and means for selectively connecting anddisconnecting said latch hook from said latch detent.
 11. A box holddown system as in claim 9 including a door hingeably mounted along theupper portion of the side of the box adjacent said hinge, said doorbeing capable of opening outwardly to provide a channel for thedischarge of cargo as the box is tilted upwardly from said first loweredposition toward said second elevated position.
 12. A box hold downsystem As in claim 9 in which the side of the box adjacent said hingeincludes a gate extending along said one lateral edge of the box, saidgate being movable between a closed position covering an elongated foreand aft opening along the lower portion of said box side and an openposition uncovering said opening.
 13. A box hold down system as in claim9 in which said hinge includes a sleeve, and a pivot pin journaled insaid sleeve and extending fore and aft along said one lateral edge ofthe box to a location adjacent said corners, the box being pivotallymounted on said pin adjacent said sleeve and adjacent the ends of saidpin, the ends of said pin being connected to said snubbing meansadjacent said corners for resiliently opposing relative verticalmovement between said corners and the underlying surface of the flatbed.
 14. A box hold down system as in claim 13 including a shockabosrber mounted on at least one end of the trailer and connected to theadjacent end of said pin, said shock absorber being inclined at anattitude such as to oppose upward vertical movement of said pin.